samos, right. I was speaking in the ancient Samosian.
Hey gimme a break As you can see, correct spelling is something that Ive never been accusewd of
Some cultures were into astrology more than three thousand years ago and they were soon making quite accurate predictions, even of eclipses of the sun and moon. The curved shadows of a partial eclipse are clues that both bodies are spherical. Likely several people formed the hypothesis that the Earth circled the sun and the moon circled the Earth but they were likely careful who they told as Earth center was the dominant opinion until the 18 th century perhaps later. The invention of the telescope helped confirm the theory when the moons of Jupiter and Saturn were observed. Most of the other posts are correct. Confidence and acceptance of the sun as the hub grew a little here and a little there over the centuries. According to Zaccariah Sitian (spell) the early Semeritans had the concept correct. Neil
fresco has it right. Copernicus demonstrated that if you assumed that the sun not the earth was the center of the "solar system, you could construct a more accurate calender for determining that date for easter. invoking the rule of parsimony this assumption also explained the periodic retrograde motion of planets and made predicting those motions easier.
fresco wrote:Forgive my perversity here but I always understood that the heliocentric system was preferred because it made the equations simpler. There is no "objective truth" and in "fact" the Sun and Earth could be considered to rotate about a common centre of gravity. This is case where "elegance" is utilized in choice of explanation.
I think that you may find that the more practical work of Newton and Einstein to be more effective than 'elegant'. If the Sun was to rotate around anything it would be the massive extra-solar object in the solar system, Jupiter.
You should all play around here
CELESTICA
while thinking :wink: (Honestly, it's a great free software, and worth downloading, I think.)
Aristarchus of Samos is known as the person who first proposed the heliocentric theory of the planetary motion (or of the earth) in ancient Greece. Copernicus presented a heliocentric model of planetary motion in his book, "De revolutionibus orbium coelestium." As it assumed the circular motion for the earth and celestial bodies, the precision of its prediction was not much an improvement over that of the geocentric model. Later Johannes Kepler presented a model of the heliocentric model where orbits are assumed to be ellipses based on the observation of Tycho Brahe. Kepler's model was an almost decisive improvement of the precision of the computation over that of the geocentric model. Galileo Galilei discovered four famous satellites of Jupiter which go around the planet with his telescope, and he was convinced of the Copernicus' model of the solar system, publishing books for advocating Copernicus' model. His view was not very popular in the catholic church then.
The Greek astronomer Ptolemy (who lived in Alexandria about AD 140) proposed a system of planetary motion in which the Earth was fixed at the centre and all the planets.
Ptolemy was able to predict the motions of the planets with considerable accuracy. His scheme was adopted as absolute dogma and survived more than 1,000 years until the time of Copernicus.
Aristachus of Samos, (c. 310-230 BC), Greek astronomer, was the first to maintain that the Earth rotates and revolves around the Sun. On this ground,Cleanthes the Stoic declared that he ought to be indicted for impiety.
Aristarchus' advanced ideas on the movement of the Earth are known from Archimedes and Plutarch; his only extant work is a short treatise, "On the Sizes and Distances of the Sun and Moon." The values he obtained, by usinggeometry, are inaccurate, because of faulty observations.
Aristarchus found a more precise value for the length of the solar year. A lunar crater is named for him; a peak in its centre is the brightest formation on the Moon.
... just adding some ecyclopaedia knowledge from the Britannica to satt's response :wink:
Geocentric system is far from dead, and is still used by astronomers because it is far simpler to use for observing.
Imagine looking at a star chart, with the night sky plotted as seen from the surface of the Sun..
Good point Relative. old models are rarely completely discarded, they are just incorporated into those that replace them.
Not only was Gallileo unpopular with the Church, he was rather stupid about it, too. He was employed by the Doges of Venice, and he was strongly advised not to leave their territory. He brushed off the warnings, wandered out of Venetian territory, and was arrested by agents of the Vatican.
That boy was his own worst enemy . . .
Let's get back to Roger's question: How did avogadro come up with his number?
A new planet?
http://news.bbc.co.uk/2/hi/science/nature/3511678.stm
"Astronomers have discovered a new world circling the Sun farther away than other planets.
"Observations show it is about 2,000 km across, and it may even be larger than Pluto which is 2,250 km across."
Satt thinks, even Pluto is doubted as a planet and the newly discoverd rock or ice adds to the doubt.
Setanta wrote:I believe that the Greeks came up with the idea long before Copernicus.
Yes. But Ptomoläus,Greek too, has refered the geocentrum idea.
fresco wrote:Forgive my perversity here but I always understood that the heliocentric system was preferred because it made the equations simpler. There is no "objective truth" and in "fact" the Sun and Earth could be considered to rotate about a common centre of gravity. This is case where "elegance" is utilized in choice of explanation.
So in my book the question is not how but why.
If you believe Newtonian mechanics, the planets and Sun all orbit the solar system's center of mass, but, because the Sun is much more massive than the planets, this is very, very close to, and perhaps even inside of, the Sun. Its precise location probably depends slightly on the configuration of the planets at that moment.
rosborne979 wrote:All I could remember was someone (Galileo I think) observing sailing ships through telescope and noticing that the masts appeared first before the bow. But this was how the Earth was confirmed to be not flat, it wasn't how Heliocentricity was determined.
I believe Francis Bacon had a similar insight in years prior to Galileo Galilei.
It's Copernicus. Ptolemy had a similar, not the same, observation.
satt_focusable wrote:It's Copernicus.
Thanks. Francis wasn't even the correct Bacon I was thinking of. I was way off the mark.
Brandon9000 wrote:If you believe Newtonian mechanics, the planets and Sun all orbit the solar system's center of mass, but, because the Sun is much more massive than the planets, this is very, very close to, and perhaps even inside of, the Sun. Its precise location probably depends slightly on the configuration of the planets at that moment.
Hi Brandon,
The center point you are talking about is called the barycenter. And in one of my favorite threads of all time (on abuzz), Satt and I discussed this, and through some web research, discovered that the barycenter not only moves into, and out of, the Sun, but also has an eleven year cycle of movement which coincides with the solar activity cycle, and may well be the *cause* of the solar cycle.
Individual wrote:Let's get back to Roger's question: How did avogadro come up with his number?
He didn't. Avogadro had a model of gases which we know as the "ideal gas". This model predicts that equal volumes of any given gas, at equal pressure and temperature, will have the same number of particles in it. Avogadro knew there was _an_ Avogadro number, but he didn't know what it was. The numerical value was determined after his death, when scientists could determine molecular masses with e/m experiments.
Sorry, gotta go.
